A. Field of the Invention
The present invention relates to audio communication transmissions, and in particular, to such transmissions wherein data bursts are contained within the transmissions, and more particularly, to an apparatus and method to improve on the audio quality of such transmissions.
B. Problems in the Art
In co-pending, co-owned U.S. Ser. No. 08/689,397, filed Aug. 7, 1996, the concerns about improving audio quality of voice communications that include bursts of digital data (e.g. synchronization data) are set out and a proposed solution is disclosed. The bursts of audio are concealed by replacing the data bursts with, for example, a piece of immediately preceding audio. Essentially, a small part of the audio is replayed during the period a data burst would otherwise exist in the audio signal.
Thus, instead of the pops, snaps, and crackles that would be heard if the data bursts were not removed and were played through with the audio, and which at best are annoying and at worst degrade the audio to a point where critical audio is lost, a more natural or smoother audio is achieved.
However, there is still room for improvement in the audio output. The insertion of a section of audio in place of the data bursts puts audio (e.g. voice) in those locations, but the audio can at times have a stuttering effect because of this play back. Even though the length of a data burst is relatively short, it can be long enough to cover critical letter or syllabic information. Thus the repetition or play back of a preceding segment of voice, for example, can create a stuttering sound that is distracting or which degrades the quality of the audio noticeably. It is therefore the principal object of the present invention to further improve the audio output over that disclosed in U.S. Ser. No. 08/689,397 and the state of the art.
Furthermore it is the object of the present invention to provide an apparatus and method for concealing data bursts in an analog scrambler:
A. which conceals the data bursts by repeating audio taken from audio portions immediately prior to and immediately after each corresponding data burst of the transmission;
B. which conceals the data bursts in a manner which reduces distracting. audio effects;
C. which improves the sound quality of the audio to a listener;
D. which is adjustable for various sizes and types of data bursts;
F. which is implementable in several fashions, including with a digital signal processor; and
G. which is economical, efficient and durable in use.
These and other objects, features, and advantages of the present invention will become more apparent with reference to the accompanying specification and claims.
The invention includes a method of concealing data bursts in a transmitted time multiplexed signal, comprising periods of scrambled audio and periods of data bursts, by replacing at an audio output the data bursts with audio taken from the audio portions of the transmitted time multiplexed signal immediately prior to and immediately after each data burst. In one aspect of the invention, the replacement of the data bursts is accomplished by storing immediate past and immediate future audio samples from the signal and playing back those audio samples during receipt of a data burst. The replay of sampled audio is correlated to the length of a data burst.
The apparatus according to the present invention utilizes storage buffers that contain audio samples of immediate past and immediate future audio portions of the signal relative to each data burst, switching devices, and a control device to allow the audio portions of the signal to pass through the switching devices to an audio output, but changing states to pass stored audio samples to the audio output at those times when a data burst otherwise would be present at the audio output. The data bursts in the signal are therefore effectively concealed.